Defect inspection apparatus and defect inspection method

ABSTRACT

A defect inspection apparatus comprises a pattern image obtaining unit obtaining a pattern image of a predetermined part by causing focusing control to be performed in order to achieve focus on the predetermined part within an observation object according to set focusing control parameters, a pattern image storing unit storing the pattern image, and a detecting unit detecting the presence/absence of an abnormal condition of a part to be inspected by making a comparison between the pattern image of a reference part within the observation object, and the pattern image of the part to be inspected within the observation object. The focusing control parameters set when the pattern image of the part to be inspected is obtained are determined based on sample information obtained when the pattern image of the reference part is obtained.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a defect inspection apparatus of a chipcomparison inspection method, which automatically detects a defect of asemiconductor wafer, and a defect inspection method.

2. Description of the Related Art

In recent years, wiring rules have been becoming minute with theinnovation of semiconductor technology, and the demand for detecting adefective chip with high accuracy at high speed has been growing in asemiconductor wafer inspection apparatus.

Accompanying this, the automation of a semiconductor wafer inspectionapparatus using a microscope has been advancing, and an AF forautomatically achieving focus on an observation object has become anessential function. The performance of the AF function included in suchan apparatus plays a very important role in improvements in, so-called,an inspection throughput (inspection efficiency per unit time).

For example, an semiconductor wafer automatic defect inspectionapparatus of a chip comparison inspection method makes a matching(pattern matching) between a pattern of a normal chip verifiedbeforehand and that of a chip to be inspected by taking advantage of thefact that a number of identical pattern chips are aligned and formed ona semiconductor wafer. If the apparatus determines that the patternsmismatch, it judges that an abnormal condition occurs in the chip to beinspected, and analyzes the contents of the abnormal condition.

With this automatic defect inspection apparatus, the AF is executedrespectively when the pattern image of the normal chip is recognized,and when the pattern image of the chip to be inspected is captured.Therefore, the apparatus requires an AF operation time by the amount oftime of the AF. Additionally, if focusing accuracy is poor, and if theimage of the normal chip or the chip to be inspected becomes, so-called,defocused, the apparatus can erroneously judge the normal chip as anabnormal chip when making the pattern matching.

In the meantime, as a technology for improving AF performance such as afocusing speed and focusing accuracy, for example, Japanese PatentPublication No. H06-165019 discloses an automatic focusing apparatusswitching a calculation method of a defocusing amount used to determinethe focusing of AF control according to the luminance of a sample.Furthermore, Japanese Patent Application Laid-open No. H11-84228discloses an automatic focus adjustment apparatus switching an algorithmof AF control according to brightness, which is an observationcondition.

SUMMARY OF THE INVENTION

A defect inspection apparatus according to one preferred embodiment ofthe present invention comprises: a pattern image obtaining unitobtaining the pattern image of a predetermined part by causing anobservation part of an observation object to be changed to thepredetermined part within the observation object, and by causingfocusing control to be performed in order to achieve focus on thepredetermined part according to set focusing control parameters; apattern image storing unit storing the pattern image obtained by thepattern image obtaining unit; and a detecting unit detecting thepresence/absence of an abnormal condition of the part to be inspectedand the contents of the abnormal condition (defect) by making acomparison between the pattern image, which is stored in the patternimage storing unit and obtained by the pattern image obtaining unit, ofa reference part determined to be normal beforehand within theobservation object, and the pattern image, which is obtained by thepattern image obtaining unit, of a part to be inspected, which becomes atarget of inspecting the presence/absence of a defect within theobservation object. The focusing control parameters, which are used forthe focusing control performed when the pattern image obtaining unitobtains the pattern image of the part to be inspected, are determinedbased on sample information obtained by the focusing control performedwhen the pattern image obtaining unit obtains the pattern image of thereference part.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 exemplifies the configuration of a microscope system according toa first preferred embodiment of the present invention;

FIG. 2 shows the details of the configurations of a first AF unit and asecond AF unit;

FIG. 3A shows the defocus characteristic of a two-partitioning detector;

FIG. 3B shows the defocus characteristic of the two-partitioningdetector;

FIG. 3C shows the defocus characteristic of the two-partitioningdetector;

FIG. 4 is a flowchart exemplifying the defect inspection process of asemiconductor wafer chip, according to the first preferred embodiment;

FIG. 5 is a flowchart exemplifying an AF control process executed inS403 or S409;

FIG. 6 exemplifies AF parameters used for AF control performed for achip to be inspected;

FIG. 7A exemplifies the characteristic of the Z position of a stage, andthe sum signal of the two-partitioning detector for a sample having adifferent reflectance;

FIG. 7B exemplifies the characteristic of the Z position of the stage,and the sum signal of the two-partitioning detector for a sample havinga different reflectance;

FIG. 8 is a flowchart exemplifying the defect inspection process of asemiconductor wafer chip, according to a second preferred embodiment;and

FIG. 9 is a flowchart exemplifying the defect inspection process of asemiconductor wafer chip, according to a third preferred embodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments according to the present inventionare explained with reference to the drawings.

FIG. 1 exemplifies the configuration of a microscope system according toa first preferred embodiment of the present invention. The microscopesystem shown in this figure is one example of the configuration of ansemiconductor wafer automatic defect inspection apparatus of a chipcomparison inspection method.

As shown in this figure, this system comprises a microscope 1, amicroscope controller 2, a host system 3, etc.

The microscope 1 comprises a light source 6 for incident-lightilluminating a sample 5, which is an observation object placed on astage movable in the upward and downward, and right and left directions(XYZ directions). Illumination light from the light source 6 is incidentto the sample 5 via an aperture stop (AS) 7, a field stop (FS) 8, a cube9 changing an observation method, and an objective lens 11 attached to arevolver 10. A pencil of light from the sample 5 passes through theobjective lens 11 and a first AF unit (AF sensor head) 12, and itsportion is guided to an eyepiece lens 14 by a tube 13. The other pencilsof light are incident to a TV camera 15 and a second AF unit (AF sensorhead) 16.

The host system 3 controls the operations of the whole of the system.For example, the host system 3 controls the microscope 1, etc. via themicroscope controller 2.

The microscope controller 2 performs actual driving control for eachelectric control part via a respectively corresponding controlling unitunder the control of the host system 3.

For example, illumination light intensity control of the light source 6is performed according to a light source control instruction from themicroscope controller 2, and a light source controlling unit 17 suppliespower according to the control instruction to the light source 6.Additionally, the control of the aperture stop 7 and that of the fieldstop 8 are performed according to control instructions from themicroscope controller 2 in a similar manner. An aperture stop (AS)controlling unit 18 drives the aperture stop 7 according to the controlinstruction, and a field stop (FS) controlling unit 19 drives the fieldstop 8 according to the control instruction. Furthermore, the drivingcontrol of the revolver 10 is performed according to a controlinstruction from the microscope controller 2 in a similar manner, and arevolver driving controlling unit 20 drives the revolver 10 according tothe control instruction. As a result, the revolver 10 is rotated, andthe magnification, etc. of the objective lens 11 on an optical path arechanged. The move control of the stage 4 is performed according tocontrol instructions from the microscope controller 2 in a similarmanner. A stage X-Y driving controlling unit 21 drives a motor 22according to the control instruction to move the stage 4 in the XYdirection, whereas a stage Z driving controlling unit 23 drives a motor24 according to the control instruction to move the stage 4 in the Zdirection.

Furthermore, an AF control function is embedded in the stage Z drivingcontrolling unit 23, which moves the stage 4 upward and downward basedon the defocus amount for the sample 5, which is detected by the firstand the second AF units 12 and 16 and will be described later, to guidethe sample 5 to a focusing position.

In the meantime, the image of the sample 5, which is captured by the TVcamera 15, is obtained by the host system 3 with a video board 25, andthe host system 3 can store the obtained image in an image memory notshown. Additionally, the host system 3 can make the ON/OFF setting ofautomatic gain control and a gain setting, and the ON/OFF setting ofautomatic exposure control and an exposure time setting for exposure inthe TV camera 15 via the TV controller 26.

FIG. 2 shows the details of the configurations of the above describedfirst AF unit 12 and second AF unit 16.

In this figure, the first AF unit 12 adopts an active AF method of apupil partitioning type, which is one of active AF methods illuminatinginfrared laser light, etc. on a sample and performing AF control byusing the light reflected from the sample. In the meantime, the secondAF unit 16 adopts a passive AF method of a mountain climbing type, whichis one of passive AF methods performing AF control by using the lightimage of a sample formed on an image capturing element such as a CCD,etc. Namely, this system adopts a hybrid AF method including the activeand the passive AF methods.

Normally, for the characteristics of the AF performance implemented byboth of the methods, the active AF method has an advantage in a focusingspeed over the passive AF method, which depends on a focal depth,whereas the passive AF method, which actually achieves focus on thelight image of a sample, has an advantage in focusing accuracy over theactive AF method, which detects a distance to a sample.

However, with the passive AF method, the presence/absence of a contrastcannot be detected if a semiconductor wafer, which becomes a sample, isa mirror surface, etc. Therefore, in this system inspecting a defect ofa semiconductor wafer, precedence is given to the active AF method inconsideration of the throughput and an adaptive sample.

In the first AF unit 12 shown in FIG. 2, a laser light source 32 emitsp-polarized laser light when a laser driving signal from a laserdriving/lens driving unit 21 is input. The p-polarized laser light isconverted into parallel pencils of light by a collimate lens 33, andpasses through a visible cut filter 34 so that visible light included inthe laser light is not irradiated on the sample 5. The pencils of lightthat pass through the visible cut filter 34 are incident to a polarizedlight beam splitter 36 via a shield 35 for shielding a half of theparallel pencils of light. The polarized beam splitter 36 has acharacteristic such that a p-polarized light component is reflected, andan s-polarized light component passes through in order to reflect thepencils of light, which are not shielded by the shield 35, by 90°. Thelaser light reflected by the polarized light beam splitter 36 passesthrough a ¼ wavelength plate 39 via an image forming system lens group37 and 38, is put into elliptically polarized light, and incident to thesample 5 via the objective lens 11 with a dichroic mirror 40 that isinstalled on the optical axis of the objective lens 11 and reflects onlythe wavelength of the laser light. In this figure, a path on which suchlaser light from the laser light source 32 is incident to the sample 5is represented by being hatched to the right.

The laser light reflected from the sample 5 returns on the incidentoptical path, is put into an s-polarized light component, which passesthrough the polarized light beam splitter 36, by the ¼ wavelength plate39, image-formed by an image forming lens 41, and incident to atwo-partitioning detector 42 of an integral photoreceptor, as shown bybeing hatched to the left in this figure. Outputs according to theincident position (outputs on sides A and B) are input to an AF defocussignal generator 30 (also referred to simply as a signal generator 30hereinafter). Then, the signal generator 30 generates a correspondingdefocus signal based on the output of the two-partitioning detector 42,and outputs the generated signal to a stage Z driving controlling unit23.

The image forming system lenses 37, 38, and 41 are configured to bemovable according to a lens driving signal from the laser driving/lensdriving unit 31. By moving any of the lenses, the wavelength of theirradiated laser light and a wavelength to be observed can be,so-called, parfocused (for example, a focus position according to thewavelength of irradiated laser light is matched with a focus positionaccording to the wavelength to be observed, or the like), or an offsetcan be provided to the focus position.

FIGS. 3A, 3B, and 3C show the defocus characteristic of thetwo-partitioning detector 42 of the first AF unit 12 thus configured.

As shown in FIG. 3A, if the sample 5 is, so-called, in a post-pinposition in which the sample 5 is under the focus position, the lightreflected from the sample 5 is incident to the side B of thetwo-partitioning detector 42, which is a photoreceptor.

Additionally, as shown in FIG. 3B, if the sample 5 is in the focusposition, the light, which has the same amount and is reflected from thesample 5, is incident to the sides A and B of the two-partitioningdetector 42.

Furthermore, as shown in FIG. 3C, if the sample 5 is, so-called, in anante-pin position in which the sample is above the focus position,contrary to the position shown in FIG. 3A, the light reflected from thesample 5 is incident to the side A of the two-partitioning detector 42.

With such a defocus characteristic, the active AF in the first AF unit12 shown in FIG. 2 is executed as follows.

The active AF defocus signal generator 30 generates a defocus signalwhich represents the amount of defocus of the sample 5 based on theoutputs of the sides A and B of the two-partitioning detector 42, andoutputs the defocus signal to the stage Z driving controlling unit 23.The stage Z driving controlling unit 23 drives the motor 24 based on thedefocus signal to move the stage 4 in the Z direction so that thedefocus amount becomes 0, namely, the outputs of the sides A and Bbecome equal. As a result, the sample 5 is guided to the focusingposition. Additionally, the signal generator 30 outputs the sum signalof the outputs of the sides A and B of the two-partitioning detector 42to the stage Z driving controlling unit 23 as occasion demands. Then,the stage Z driving controlling unit 23 can determine whether or not thesample 5 is close to the focusing position.

In the meantime, in the second AF unit 16 shown in FIG. 2, the lightimage of the sample is returned by a half mirror 51, and formed on a CCDsensor 53 by an image forming lens 52. The output of the CCD sensor 53is input to a passive AF defocus signal generator 50 (also referred tosimply as a signal generator 50 hereinafter). Then, the signal generator50 generates a corresponding defocus signal based on the output of theCCD sensor 53, and outputs the generated signal to the stage Z drivingcontrolling unit 23.

The passive AF in the second AF unit 16 having such a configuration isexecuted as follows.

The passive AF defocus signal generator 50 performs a known contrastoperation such as the integral value of a difference between adjacentpixels based on an image signal (the output of the CCD sensor 53)captured by the CCD sensor 53, and outputs the result of the contrastoperation to the stage Z driving controlling unit 23 as a defocussignal. The stage Z driving controlling unit 23 drives the motor 24based on the defocus signal (the result of the contrast operation) tomove the stage 4 in the Z direction so that the contrast of the imageprojected on the CCD sensor 53 becomes a maximum. As a result, thesample 5 is guided to the focusing position.

Additionally, the defocus signal generated by the signal generator 30with the active AF, and the defocus signal (the result of the contrastoperation) generated by the signal generator 50 with the passive AF are,as described above, input to the stage Z driving controlling unit 23,which can use each AF method depending on a use purpose, or can detectthe defocus state implemented with the passive AF while executing theactive AF.

Additionally, the stage Z driving controlling unit 23 includes a memory(not shown) for storing data, and can store various types of data (AFparameters, etc.) about the AF control, which are output from the hostsystem 3.

A defect inspection process of a semiconductor wafer chip is explainednext as one of control processes executed by the host system 3 of themicroscope system configured as described above.

FIG. 4 is a flowchart exemplifying the defect inspection process.

In this figure, a semiconductor wafer, which becomes a sample, is placedon the stage 4. Once the defect inspection process is started, the stage4 is first moved to a preset reference chip position in step S401. Thereference chip is a chip that is verified to be normal beforehand.

In S402, default values are set as AF parameters used for the AF controlfor the reference chip. Note that the default values are valuesconsidered to allow the AF control to be performed for every sample.Examples of the AF parameters include a stage speed when the AF controlis performed, a stage Z range (search range), a passive AF contrastthreshold value (a first predetermined value), etc., which will bedescribed later.

In step S403, the AF control for the reference chip is started accordingto the AF parameters set in the preceding step, and focus is achieved.The AF control performed in this step will be described later withreference to FIG. 5.

In step S404, AF parameters (AF parameters for feedback) used for the AFcontrol for a chip to be inspected, which is performed next, areobtained based on sample information obtained by the AF controlperformed in the preceding step. The sample information is information,for example, about the focusing position of the reference chip, theamount of light according to the light reflected from the referencechip, and the like. Additionally, the AF parameters to be obtained areparameters optimum for obtaining a fast focusing speed, and highfocusing accuracy in the AF control performed for the chip to beinspected. Examples of these AF parameters include a stage speed and astage Z range (search range), etc. optimum for obtaining a high focusingspeed, a passive AF contrast threshold value (a first predeterminedvalue) optimum for obtaining high focusing accuracy, and the like. SuchAF parameters obtained in this step will be described later withreference to FIG. 6.

In S405, the image of the reference chip, the focus of which is achievedin S403, is obtained via the video board 25.

In S406, the image of the reference chip, which is obtained in thepreceding step, is stored in the memory of the host system 3.

When the image of the reference chip is thus obtained, the obtainment ofthe image of the chip to be inspected is started.

Firstly, in S407, the stage 4 is moved to the position of the chip to beinspected.

In S408, the AF parameters obtained in the above described S404 (the AFparameters for feedback) are set as the AF parameters used for the AFcontrol for the chip to be inspected.

In S409, the AF control for the chip to be inspected is startedaccording to the AF parameters set in the preceding step, and focus isachieved. The AF control performed in this step will be described laterwith reference to FIG. 5.

In S410, the image of the chip to be inspected, the focus of which isachieved in the preceding step, is obtained via the video board 25.

In S411, a matching between the pattern of the image of the referencechip, which is stored in the above described S406, and that of the imageof the chip to be inspected, which is obtained in the preceding step, ismade. If the patterns mismatch, the chip to be inspected is determinedto be an abnormal chip. If the patterns match, the chip to be inspectedis determined to be a normal chip. Namely, the presence/absence of adefect, and the contents of the defect are diagnosed in this step. Thecontents of the defect are, for example, a disconnection of a wiringpattern, the adhesion of dust, etc.

In S412, it is determined whether or not a chip to be inspected, whichis yet to be inspected, is left. If the result of the determination is“Yes”, the flow goes back to S401. If the result of the determination is“No”, this flow is terminated. With such a determination, the abovedescribed process is repeatedly executed until a chip to be inspected,which is yet to be inspected, is not left.

The flow shown in FIG. 4 is executed, so that the AF parameters optimumfor improving the focusing speed and the focusing accuracy in the AFcontrol for a chip to be inspected are set based on sample informationobtained by the AF control for the reference chip. Accordingly,high-speed and highly accurate AF control can be performed for a chip tobe inspected, and high defect detection accuracy and a high throughputcan be implemented in the defect inspection of a semiconductor wafer.

In this flow, the image of the reference chip and that of the chip to beinspected are obtained alternately. However, images of a plurality ofchips to be inspected may be obtained for the image of a singlereference chip, and a pattern matching with the image of each of thechips to be inspected may be made by using the image of the singlereference chip.

FIG. 5 is a flowchart exemplifying the AF control process executed inthe above described S403 or S409.

In this figure, once the AF control is started, the stage 4 is firstmoved to the lower limit position, which is set as one of the AFparameters, of the stage Z range (search range) for which the AF controlis performed in S501.

In S502, the move of the stage 4 is started in the direction of theupper limit position of the above described stage Z range at a stagespeed SP1 set as one of the AF parameters.

In S503, it is determined whether or not the stage 4 reaches the upperlimit position of the above described stage Z range. If the result ofthe determination is “Yes”, the flow goes to S510. If the result of thedetermination is “No”, the flow goes to S504.

In S504, it is determined whether or not a contrast value according tothe defocus signal (a result of a contrast operation) output from thepassive AF defocus signal generator 50 is equal to or larger than thefirst value predetermined as one of the AF parameters. If the result ofthe determination is “Yes”, the flow goes to S505. If the result of thedetermination is “No”, the flow goes to S506.

In step S505, the position (stage address) of the stage 4 at this timeis stored as Z1.

In S506, it is determined whether or not the sum signal of the outputsof the sides A and B of the two-partitioning detector 42, which isoutput from the active AF defocus signal generator 30, is equal to orlarger than the second value predetermined as one of the AF parameters.If the result of the determination is “Yes”, the stage 4 is determinedto be close to the focusing position, and the flow goes to S507. If theresult of the determination is “No”, the stage 4 is determined to be farfrom the focusing position, and the flow goes back to S503.

As described above, with this system, the determination of whether ornot the stage 4 is close to the focusing position is made with theresult of the detection made by the first AF unit 12 by givingprecedence to the active AF method. This is because if a semiconductorwafer, which becomes a sample, is a mirror surface, etc., thepresence/absence of a contrast cannot be detected with the passive AFmethod, and a proper determination cannot possibly be made.

In S507, focusing is achieved by the first AF unit 12 with the active AFmethod. Namely, the position of the stage 4 is controlled so that theoutputs of the sides A and B of the two-partitioning detector 42 becomeequal, and the focusing is achieved by the first AF unit 12 with theactive AF method.

In S508, the defocus signal (the result of the contrast operation)output from the passive AF defocus signal generator 50 is obtained inthe position of the stage 4 when the focusing is achieved in thepreceding step, and it is determined whether or not the contrast valueaccording to the defocus signal is equal to or larger than the abovedescribed first predetermined value. If the result of the determinationis “Yes”, the flow goes to S509. If the result of the determination is“No”, the flow is terminated.

In S509, the stage 4 is moved so that the contrast value according tothe defocus signal output from the passive AF defocus signal generator50 becomes a maximum. Namely, the focusing is achieved by the second AFunit 16 with the passive AF method, and this flow is terminated.

In the meantime, the above described processes in S503 to S506 arerepeated, and the sum signal of the outputs of the sides A and B of thetwo-partitioning detector 42 does not become equal to or larger than thesecond predetermined value in the whole of the stage Z range (searchrange), for which the AF control is performed, namely, if the result ofthe determination in the above described S503 is “Yes”, it is determinedin the succeeding S510 whether or not there is a position of the stage4, in which the contrast value according to the defocus signal outputfrom the passive AF defocus signal generator 50 is equal to or largerthan the first predetermined value in the processes in S503 to S506executed in the whole of the stage Z range, namely, whether or not thereis the position of the stage 4, which is stored as Z1 in the abovedescribed S505. If the result of the determination is “Yes”, the flowgoes to S511. If the result of the determination is “No”, the flow goesto S512.

In S511, the stage 4 is moved to the position stored as Z1, and the flowgoes to the above described S509, in which the focusing is achieved withthe passive AF method.

In S512, the move of the stage 4 is started in the direction of thelower limit position of the above described stage Z range at a stagespeed SP2 set as one of the AF parameters. However, this stage speed SP2is set as a speed lower than the stage speed SP1 in order to increasethe possibility of achieving the focus.

In S513, it is determined whether or not the stage 4 reaches the lowerlimit position. If the result of the determination is “Yes”, this flowis terminated. If the result of the determination is “No”, the flow goesto S514.

In S514, it is determined whether or not the contrast value according tothe defocus signal (the result of the contrast operation) output fromthe passive AF defocus signal generator 50 is equal to or larger thanthe above described first predetermined value. If the result of thedetermination is “Yes”, the flow goes to S509, in which the focusing isachieved with the passive AF method. If the result of the determinationis “No”, the flow goes back to S513. In this way, this determination isrepeated until the contrast value is determined to be equal to or largerthan the first predetermined value up to when the stage 4 reaches thelower limit position of the stage Z range.

As described above, the flow shown in FIG. 5 is executed, whereby the AFcontrol is performed according to the default values set in the abovedescribed S402, or the AF parameters for feedback, which are set inS408, as the AF parameters. Additionally, when the AF control isperformed according to the AF parameters for feedback, high-speed andhighly accurate AF control can be implemented. This is because theparameters are optimum values for obtaining a fast focusing speed andhigh focusing accuracy.

The control for detecting whether or not the sum signal of the outputsof the sides A and B of the two-partitioning detector 42 is equal to orlarger than the second predetermined value while moving the stage 4 iscalled sample capturing control using the active AF method, whereas thecontrol for detecting whether or not the contrast value according to thedefocus signal output from the passive AF defocus signal generator 50 isequal to or larger than the first predetermined while moving the stage 4is called sample capturing control using the passive AF method.

The AF parameters, which are obtained based on the sample informationacquired with the AF control performed for the above described referencechip and used for the AF control performed for the chip to be inspected,are described next.

FIG. 6 exemplifies the AF parameters.

In this figure, an active AF stage speed indicates the fastest stagespeed at which a sample search can be made when the sample search ismade with the active AF method, namely, the fastest stage speed at whichsample capturing can be made when the sample capturing control using theactive AF method is performed, and is an AF parameter that contributesto an improvement in the focusing speed. This is obtained based on theamount of light (sample information) reflected from the sample, which isobtained when the AF control is performed for the reference chip. In theexplanation of FIG. 5, this active AF stage speed is defined as thestage speed SP1 when the AF control for the chip to be inspected isperformed. This stage speed will be described in detail later withreference to FIGS. 7A and 7B.

Additionally, a search range indicates the minimum stage Z range (therange of the stage 4 in the Z direction), for which the sample capturingcan be made when the AF control is performed, and is an AF parameterthat contributes to an improvement in the focusing speed. This isobtained based on the focusing position (sample information) obtainedwhen the AF control is performed for the reference chip, and a range inthe vicinity of the focusing position of the reference chip is definedas the search range for the chip to be inspected when the AF control isperformed.

For example, if the focusing position of the sample is completelyunknown, the AF control must be performed by setting an extensive searchrange. With this system, however, the focusing position of the chip tobe inspected can be identified to some extent by detecting the focusingposition with the AF control for the reference chip. Therefore, with theAF control for the chip to be inspected, the stage Z range when the AFcontrol for the chip to be inspected is performed can be set to a narrowrange by using a vicinity of the focusing position of the reference chipas the search range, whereby the focusing speed can be improved byreducing the search time. In the explanation of FIG. 5, this searchrange is defined as the stage Z range when the AF control is performedfor the chip to be inspected.

Additionally, a sample search AF method indicates any of the active AFmethod, the passive AF method, and the hybrid AF method as an AF methodwhen a sample is searched, and is an AF parameter that contributes to animprovement in the focusing speed.

For example, if the sum signal of the outputs of the sides A and B ofthe two-partitioning detector 42 is not determined to be equal to orlarger the second predetermined value as a result of performing the AFcontrol for the reference chip in the flows shown in FIGS. 4 and 5 (“No”in S506), the possibility that the sum signal of the outputs of the chipto be inspected is determined to be equal to or larger than the secondpredetermined value is also considered to be low. Accordingly, thesample search AF method when the AF control for the chip to be inspectedis performed is limited to the passive AF method based on the sampleinformation obtained when such AF control for the reference chip isperformed, whereby the sample search using the active AF in method canbe made not to be performed when the AF control is performed for thechip to be inspected is performed, and a meaningless process can beprevented from being executed. As a result, the focusing speed can beimproved.

Additionally, a passive AF stage speed indicates the fastest stage speedat which the sample search can be made when the sample search using thepassive AF method is made, namely, the fastest stage speed at whichsample capturing can be made when the sample capturing control using thepassive AF method is performed, and is an AF parameter that contributesto an improvement in the focusing speed. This is obtained based on theamount of light (sample information) reflected from the sample, which isobtained when the AF control for the reference chip is performed. In theexplanation of FIG. 5, the passive AF stage speed is defined as thestage speed SP2 when the AF control for the chip to be inspected isperformed. However, as described above, the stage speed SP2 is definedas a speed lower than the stage speed SP1 in order to increase thepossibility of achieving focusing. The stage speed will be described indetail later with reference to FIGS. 7A and 7B.

Additionally, an active AF offset amount indicates the offset amount atthe focusing position when the AF control using the active AF method isperformed, and is an AF parameter that contributes to an improvement inthe focusing accuracy. The active AF offset amount is not obtained bythe AF control for the reference chip, but set, for example, by a personwho makes a measurement.

For example, when focusing is achieved with the active AF method for thechip to be inspected if a film is coated on either the reference chip orthe chip to be inspected, high focusing accuracy can be secured byoffsetting the thickness of the film from the focusing position based onthe active AF offset amount.

Additionally, a passive AF contrast threshold value indicates athreshold value optimum for detecting the presence/absence of acontrast, and contributes to an improvement in the focusing accuracy.This is obtained based on the amount of light (sample information)reflected from the sample, which is obtained when the AF control for thereference chip is performed. In the explanation of FIG. 5, the passiveAF contrast threshold value is defined as the first predetermined value.

Here, the above described stage speed when the AF control is performedfor the chip to be inspected is performed is further explained in detailin order to deepen understanding.

FIGS. 7A and 7B exemplify the characteristic of the Z position of thestage 4 and the sum signal of the two-partitioning detector 42 forsamples having different reflectances. FIG. 7A shows the characteristicof a sample having high reflectance, whereas FIG. 7B shows thecharacteristic of a sample having low reflectance. In FIGS. 7A and 7B,the horizontal axis indicates a Z coordinate (the Z position of the Zstage 4), and the vertical axis indicates the sum signal of thetwo-partitioning detector 42. Additionally, the position in which the Zcoordinate is 0 indicates the focusing position, and indicates aposition in which the light reflected from the sample is the highest.

As shown in FIGS. 7A and 7B, a difference between the reflectances ofthe samples is a difference between ranges where the light reflectedfrom the samples can be detected in the Z direction of the stage 4.Assuming that the level of the sum signal, at which a sample isdetermined to be close to the focusing position from the S/N, etc. ofthe signal, is Pth, the capturing range of the sample having the highreflectance, which is shown in FIG. 7A, is X1, and the capturing rangeof the sample having the low reflectance, which is shown in FIG. 7B, isX2, and the ranges have proportionalities with the reflectances. For thesample having the high reflectance, the sample capturing can beperformed in a position more apart from the focusing position than thesample having the low reflectance.

In the sample capturing control, the stage speed when a sample iscaptured has a close relationship with this sample capturing range. Thewider the sample capturing range, the higher the stage speed can beimproved. As a result, a fast focusing speed can be obtained.Accordingly, the stage speed must be set to the lowest by assuming thecase where the reflectance of an unknown sample is the lowest within thespecifications by which the AF control can be performed for the sample,when the AF control is made for an unknown sample. If the reflectance ofa sample is detected when the AF control for the reference chip isperformed as in this system, and if it is known, a suitable stage speedcan be set according to the detected reflectance of the sample when theAF control is performed for the chip to be inspected, so that thefocusing speed can be improved.

As described above, according to this preferred embodiment, in thesemiconductor wafer automatic defect inspection apparatus of a chipcomparison inspection method, fast and highly accurate AF control can beperformed for a chip to be inspected by feeding back the sampleinformation obtained by the AF control for the reference chip when theAF control is performed for the chip to be inspected, whereby theinspection accuracy and the throughput can be dramatically improved.

To this preferred embodiment, the hybrid AF method that respectivelyadopts the pupil partitioning type and the mountain climbing type as theactive AF method and the passive AF method is applied. However, it isnot necessary that the AF method is the hybrid method in the controlprocess for feeding back the sample information obtained when the AFcontrol for the reference chip is performed, when the AF control for thechip to be inspected is performed. A similar effect can be obtained alsoby replacing the AF method referred to in this preferred embodiment witha known AF method.

Additionally, this preferred embodiment is configured so that the sampleis guided to the focusing by moving the stage 4 on which the sample isplaced in the Z direction (upward and downward directions). However, asimilar effect can be obtained also with a configuration such that thesample is guided to the focusing position by moving the objective lens11 in the Z direction.

Furthermore, this preferred embodiment is configured so that theobservation part of the sample is changed by moving the stage 4 on whichthe sample is placed in the XY direction (right and left directions)However, a similar effect can be obtained also with a configuration suchthat the observation part of the sample is changed by moving theobjective lens 11 in the XY direction.

A second preferred embodiment according to the present invention isexplained next.

The configuration of a microscope system according to this preferredembodiment is similar to that shown in FIGS. 1 and 2. However, a defectinspection process of a semiconductor wafer chip, which is one ofcontrol processes, is different from that shown in FIG. 4. Here, thedefect inspection process is explained.

FIG. 8 is a flowchart exemplifying the defect inspection process of asemiconductor wafer chip, according to the second preferred embodiment.

In this figure, in S801 to S804, processes similar to those in the abovedescribed S401 to S404 are executed.

In S805, a position in which focusing is achieved in S803, namely, thefocusing position Zp of the reference chip is stored. Additionally, theimage of the reference chip, for which focusing is achieved at thistime, is obtained via the video board 25, and stored in the memory ofthe host system 3.

In S806, the stage 4 is moved to the position of the chip to beinspected.

In S807, AF parameters (AF parameters for feedback), which are obtainedin S804, are set as AF parameters for the AF control performed for thechip to be inspected.

In S808, the AF control for the chip to be inspected is startedaccording to the AF parameters set in the preceding step, and focusingis achieved. The AF control in this step is performed according to theabove described flow shown in FIG. 5 (the same control is performed inS812).

In S809, it is determined whether or not the focus is properly achievedin the preceding step, namely, whether or not the focus is successfullyachieved for the chip to be inspected. If the result of thedetermination is “Yes”, the flow goes to S810. If the result of thedetermination is “No”, the flow goes to S811.

In S810, the image of the chip to be inspected at this time is obtainedvia the video board 25. A matching between the pattern of the image ofthe reference chip, which is stored in the above described S805, andthat of the image of the chip to be inspected, which is obtained in thisstep, is made. If the patterns mismatch, the chip to be inspected isdetermined to be an abnormal chip. If the patterns match, the chip to beinspected is determined to be a normal chip. Namely, thepresence/absence of a defect, and the contents of the defect arediagnosed.

In the meantime, if the AF control for the chip to be inspected isunsuccessfully performed, namely, if the result of the determinationmade in S809 is “No”, the set AF parameters are initiated to defaultvalues in the succeeding S811. Namely, the AF parameters for feedbackset as the AF parameters are destroyed and reset to the default values,whereby the AF parameters are changed from the AF parameters forfeedback to the default values.

In S812, the AF control is restarted according to the default settingsmade in the preceding step, and focus is achieved.

In S813, it is determined whether or not the focus is properly achievedin the preceding step, namely, whether or not the focusing issuccessfully achieved for the chip to be inspected. If the result of thedetermination is “Yes”, the flow goes to the above described S810. Ifthe result of the determination is “No”, the flow goes to S814.

In S814, the stage 4 is moved to the stage position Z stored in theabove described S805. This step is a process executed to obtain theimage of the chip to be inspected by regarding the focusing position ofthe reference chip as the focusing position of the chip to be inspected,because the focusing is unsuccessfully achieved in both of the AFcontrol according to the AF parameters for feedback and that accordingto the default values.

In S815, information about the unsuccessful focusing achievement(unsuccessful AF control) for the chip to be inspected is added to theimage of the chip to be inspected, which is to be obtained in S810, andthe flow goes to S810. As a result, the information about theunsuccessful focusing achievement is added to the obtained image of thechip to be inspected in the succeeding step S810. Thereafter, it can benotified that the defect detection accuracy of the image can be possiblylow.

As described above, according to this preferred embodiment, in thesemiconductor wafer automatic defect inspection apparatus of the chipcomparison inspection type, even when a chip abnormal condition, whichmakes the AF control difficult, such as the occurrence of a throughhole, the existence of a large foreign substance, etc. in the chip to beinspected occurs, the defect detection can be securely made. As aresult, the detection accuracy and the throughput can be dramaticallyimproved.

A third preferred embodiment according to the present invention isexplained next.

The configuration of a microscope system according to this preferredembodiment is similar to that shown in FIGS. 1 and 2. However, a defectinspection process of a semiconductor wafer chip, which is one ofcontrol processes, is different from that shown in FIG. 4 or 8.Accordingly, that defect inspection process is explained here.

FIG. 9 is a flowchart exemplifying the defect inspection process of asemiconductor wafer chip, according to the third preferred embodiment.

In this figure, a semiconductor wafer, which becomes a sample, is placedon the stage 4. Once the defect inspection process is started, areference chip verified to be normal is first selected in S901, and thestage 4 is moved to the position of the reference chip.

In S902, default values are set as AF parameters used for the AF controlperformed for the reference chip, and the AF control is performedaccording to the default values. It is then determined whether or notfocusing is successfully achieved (whether or not a focusing operationis properly completed). If the result of the determination is “Yes”(“OK”in this figure), the flow goes to S903. If the result of thedetermination is “No” (“NG” in this figure), the flow goes to S908. Thedefault values are as described above in the explanation of the firstpreferred embodiment. Additionally, the AF control in this step isperformed according to the flow shown in FIG. 5.

In S903, the aperture diameter of an aperture stop 7, and a voltage setin the light source controlling unit 17, which are optical parametersfor controlling the amount of illumination light irradiated on thesemiconductor wafer, are obtained and stored. The amount of theillumination light emitted from the light source 6 is controlledaccording to the voltage set in the light source controlling unit 17.

Additionally, in this step, AF parameters (AF parameters for feedback)used for the AF control performed for the chip to be inspected areobtained based on sample information obtained by the AF controlperformed in the preceding step. The AF parameters are as describedabove in the explanation of the first preferred embodiment.

In S904, for the TV camera 15, the ON setting of automatic gain controlis made, and at the same time, the ON setting of automatic exposurecontrol is made. Then, image capturing is performed for the referencechip, so that the image of the reference chip is obtained.

In S905, a gain adjustment value and exposure time when the imagecapturing is performed in the preceding step are obtained and stored.

In S906, the stage 4 is moved to the position of the next chip, namely,the position of the chip to be inspected.

In S907, the AF control for the chip to be inspected is performedaccording to the AF parameters obtained in the above described S903, andit is determined whether or not the focusing is successfully achieved(whether or not the focusing operation is properly completed). If theresult of the determination is “Yes” (“OK” in this figure), the processgoes to S909. If the result of the determination is “No” (“NG” in thisfigure), the flow goes to S908. The AF control in this step is performedaccording to the flow shown in FIG. 5.

In S908, a warning display is made since the focusing is unsuccessfullyachieved. As a result, the process is aborted, and the flow isterminated.

In S909, the aperture diameter and the voltage, which are the opticalparameters stored in the above described S903, are set in the aperturestop 7 and the light source controlling unit 17.

In S910, the gain adjustment value and the exposure time, which arestored in the above described S905, are set in the TV camera 15.

In S911, image capturing is performed for the chip to be inspected, andthe image of the chip to be inspected is obtained.

In S912, a matching between the pattern of the image of the referencechip, which is obtained in S904, and that of the image of the chip to beinspected, which is obtained in the preceding step, is made, and thepresence/absence of a defect and the contents of the defect arediagnosed.

In S913, it is determined whether or not a chip to be inspected, whichis yet to be inspected, is left. If the result of the determination is“Yes”, the flow goes back to S906, in which the process for the nextchip to be inspected is started. If the result of the determination is“No”, this flow is terminated.

As described above, the flow shown in FIG. 9 is executed, so that theimage capturing conditions of the reference chip and the chip to beinspected can be made to match. As a result, an ideal pattern matchingcan be made, and the defect detection can be made with higher accuracy.

As described above, according to this preferred embodiment, in thesemiconductor wafer automatic defect inspection apparatus of a chipcomparison inspection method, the image capturing conditions of areference chip and a chip to be inspected can be further made to match,whereby the inspection accuracy and the throughput can be dramaticallyimproved.

In the pattern matching process in this preferred embodiment, only adefective chip may be detected and output by giving precedence to theshortening of the inspection time. Additionally, the image of thedefective chip may be stored with high resolution at that time.Furthermore, detailed image information can be securely saved, forexample, if a memory, a RAM, etc. of a hard disk device, which is alarge-capacity storage medium, or a portable storage medium such as aDVD-RAM, an MO, a CD-R, etc. is used as a storage medium in which theimage is to be stored. Still further, if not a custom format but anormal image format such as JPEG, BMP, GIF, TIFF, etc. is applied as theformat of an image stored onto these storage media, a defect position, adefect state, etc. can be analyzed with general image processingsoftware. As a result, such an image processing function is omitted fromthis system, which can be configured cheaply.

A modification example of the microscope system according to thispreferred embodiment is explained next.

Configuration of the microscope system according to this modificationexample is almost similar to that shown in FIGS. 1 and 2. However, adifference exists in a point that the light source controlling unit 20newly comprises a photodetector for monitoring the output (illuminationintensity) of the light source 6. Additionally, a defect inspectionprocess of a semiconductor wafer chip, which is one of control processesof this system, is almost similar to that shown in FIG. 9. However, adifference exists in a point that the voltage obtained/stored in theabove described S903 is not the voltage set in the light sourcecontrolling unit 17, but an opto-electrically converted value accordingto the output of the light source 6, which is obtained by the abovedescribed photodetector.

As described above, according to this modification example, the changeamount of the output of the light source 6, which varies with time, canbe corrected, whereby a more accurate amount of light can be given tothe semiconductor wafer. Accordingly, the uniformity of more accurateimage capturing conditions can be secured, and the defect detection withhigher accuracy can be made.

As described above, the defect inspection apparatus and the defectinspection method according the present invention are explained indetail. However, the present invention is not limited to the abovedescribed preferred embodiments. Various types of improvements andmodifications can be made in a scope which does not deviate from thegist of the present invention, as a matter of course.

As described above in detail, according to the present invention, in thesemiconductor wafer automatic defect inspection apparatus of a chipcomparison inspection method, the defect inspection accuracy and thethroughput can be dramatically improved.

1. A defect inspection apparatus, comprising: an observation partchanging unit changing an observation part of an observation object bydriving a stage on which the observation object is placed, or anobjective lens as opposed to the observation object; a focus directiondriving unit driving at least one of the stage and the objective lens inorder to achieve focus on the observation object placed on the stage; afocusing controlling unit performing focusing control by making saidfocus direction driving unit drive at least one of the stage and theobjective lens in order to achieve focus on the observation object; afocusing control parameter setting unit setting focusing controlparameters used for the focusing control performed by said focusingcontrolling unit; a pattern image obtaining unit obtaining a patternimage of a predetermined part by making said observation part changingunit drive the stage or the objective lens in order to change theobservation part of the observation object to the predetermined partwithin the observation object, and by making said focusing controllingunit perform the focusing control according to the focusing controlparameters set by said focusing control parameter setting unit in orderto achieve focus on the predetermined part; a pattern image storing unitstoring the pattern image obtained by said pattern image obtaining unit;and a detecting unit detecting presence/absence of an abnormal conditionof a part to be inspected by making a comparison between a patternimage, which is stored in said pattern image storing unit and obtainedby said pattern image obtaining unit, of a reference part determined tobe normal beforehand within the observation object, and a pattern image,which is obtained by said pattern image obtaining unit, of the part tobe inspected, which becomes a target of inspecting presence/absence of adefect within the observation object, wherein the focusing controlparameters, which are used for the focusing control performed when saidpattern image obtaining unit obtains the pattern image of the part to beinspected, are determined based on sample information obtained by thefocusing control performed when said pattern image obtaining unitobtains the pattern image of the reference part.
 2. The defectinspection apparatus according to claim 1, wherein if the focusingcontrol is unsuccessfully performed as a result of causing the focusingcontrol to be performed when said pattern image obtaining unit obtainsthe pattern image of the part to be inspected, the focusing controlparameters are changed to default values, and the pattern image of thepart to be inspected is obtained by performing the focusing controlaccording to the focusing control parameters, which are the defaultvalues.
 3. The defect inspection apparatus according to claim 2, whereinif the focusing control is unsuccessfully performed as a result ofcausing the focusing control to be performed when said pattern imageobtaining unit obtains the pattern image of the part to be inspected,the pattern image of the part to be inspected is obtained by regarding afocusing position obtained by the focusing control performed when saidpattern image obtaining unit obtains the pattern image of the referencepart as a focusing position of the part to be inspected.
 4. The defectinspection apparatus according to claim 3, wherein when said patternimage obtaining unit obtains the pattern image of the part to beinspected by regarding the focusing position of the reference part asthe focusing position of the part to be inspected, information aboutunsuccessful focusing control is added to the pattern image of the partto be inspected.
 5. The defect inspection apparatus according to claim1, wherein said pattern image obtaining unit comprises a referencepattern image obtaining unit obtaining the pattern image of thereference part by making said observation part changing unit drive thestage or the objective lens in order to change the observation part ofthe observation object to the reference part determined to be normalbeforehand within the observation object, and by making said focusingcontrolling unit perform the focusing control according to the focusingcontrol parameters in order to achieve focuse on the reference partaccording to the focusing control parameters set by said focusingcontrol parameter setting unit, and an inspection target pattern imageobtaining unit obtaining the pattern image of the part to be inspectedby making said observation part changing unit drive the stage or theobjective lens in order to change the observation part of theobservation object to the part to be inspected, which becomes a targetof inspecting presence/absence of a defect within the observationobject, and by making said focusing controlling unit perform thefocusing control in order to achieve focus on the part to be inspectedaccording to the focusing control parameters set by said focusingcontrol parameter setting unit.
 6. The defect inspection apparatusaccording to claim 5, wherein: the focusing control parameters used forthe focusing control performed when said reference pattern imageobtaining unit obtains the pattern image of the reference part arefocusing control parameters, which are default values; and the focusingcontrol parameters used for the focusing control performed when saidinspection target pattern image obtaining unit obtains the pattern imageof the part to be inspected are focusing control parameters determinedbased on the sample information.
 7. The defect inspection apparatusaccording to claim 1, wherein the sample information is at least any ofinformation about the focusing position of the reference part andinformation about a light amount according to light reflected from thereference part.
 8. A defect inspection apparatus, comprising: a patternimage obtaining unit obtaining a pattern image of a predetermined partby causing an observation part of an observation object to be changed tothe predetermined part within the observation object, and by causingfocusing control to be performed in order to achieve focus on thepredetermined part according to set focusing control parameters; apattern image storing unit storing the pattern image obtained by saidpattern image obtaining unit; a detecting unit detectingpresence/absence of an abnormal condition of a part to be inspected bymaking a comparison between a pattern image, which is stored in saidpattern image storing unit and obtained by said pattern image obtainingunit, of a reference part determined to be normal beforehand within theobservation object, and a pattern image, which is obtained by saidpattern image obtaining unit, of the part to be inspected, which becomesa target of inspecting presence/absence of a defect within theobservation object, wherein the focusing control parameters, which areused for the focusing control performed when said pattern imageobtaining unit obtains the pattern image of the part to be inspected,are determined based on sample information obtained by focusing controlperformed when said pattern image obtaining unit obtains the patternimage of the reference part.
 9. A defect inspection method, comprising:driving a stage or an objective lens as opposed to an observation objectin order to change an observation part of the observation object placedon the stage to a reference part determined to be normal beforehandwithin the observation object; performing focusing control so thatfocusing is achieved on the reference part according to a first focusingcontrol parameter; determining a second focusing control parameter basedon sample information obtained by the focusing control; obtaining apattern image of the reference part; driving the stage or the objectivelens in order to change the observation part of the observation objectto a part to be inspected, which becomes a target of inspectingpresence/absence of a defect within the observation body; performing thefocusing control in order to achieve focus on the part to be inspectedaccording to the second focusing control parameter; obtaining a patternimage of the part to be inspected; and detecting presence/absence of anabnormal condition of the part to be inspected by making a comparisonbetween the pattern image of the reference part and the pattern image ofthe part to be inspected.
 10. The defect inspection method according toclaim 9, wherein if the focusing control is unsuccessfully performed asa result of performing the focusing control such that focusing isachieved on the part to be inspected according to the second focusingcontrol parameter, the focusing control is performed so that focusing isachieved on the part to be inspected according to the first focusingcontrol parameter.
 11. The defect inspection method according to claim10, wherein if the focusing control is unsuccessfully performed as aresult of performing the focusing control such that the focusing isachieved on the part to be inspected according to the first focusingcontrol parameter, the focusing position obtained by the focusingcontrol performed for the part to be referenced is regarded as thefocusing position of the part to be inspected, and the pattern image ofthe part to be inspected is obtained.
 12. The defect inspection methodaccording to claim 11, wherein when the pattern image of the part to beinspected is obtained by regarding the focusing position of thereference part as the focusing position of the part to be inspected,information about unsuccessful focusing control is added to the patternimage of the part to be inspected.
 13. A defect inspection apparatus,comprising: an illuminating unit illuminating an observation object; anillumination intensity controlling unit controlling an intensity ofillumination made by said illuminating unit; an image capturing unitperforming image capturing, and obtaining an image of the observationobject; an image capturing controlling unit controlling any of exposure,a gain, and exposure and a gain when the image capturing is performed bysaid image capturing unit; an observation part changing unit changingthe observation part of the observation object by driving a stage onwhich the observation object is placed, or an objective lens as opposedto the observation object; a focus direction driving unit driving atleast one of the stage and the objective lens in order to achieve focuson the observation object placed on the stage; a focusing controllingunit performing focusing control by making said focus direction drivingunit drive at least one of the stage and the objective lens in order toachieve focus on the observation object; a pattern image obtaining unitobtaining a pattern image of a predetermined part by making saidobservation part changing unit drive the stage or the objective lens inorder to change the observation part of the observation object to apredetermined part of the observation object, and by making saidfocusing controlling unit perform the focusing control in order toachieve focus on the predetermined part; a pattern image storing unitstoring the pattern image obtained by said pattern image obtaining unit;and a detecting unit detecting presence/absence of an abnormal conditionof a part to be inspected by making a comparison between a patternimage, which is stored in said pattern image storing unit and obtainedby said pattern image obtaining unit, of a reference part determined tobe normal beforehand within the observation object, and a pattern image,which is obtained by said pattern image obtaining unit, of the part tobe inspected, which becomes a target of inspecting presence/absence of adefect within the observation object, wherein any of said illuminationcontrolling unit, said image capturing controlling unit, saidilluminating unit and said image capturing controlling unit iscontrolled so that brightness of the pattern image of the referencepart, which is obtained by said pattern image obtaining unit, andbrightness of the pattern image of the part to be inspected match orapproximately match.
 14. The defect inspection apparatus according toclaim 13, further comprising a photodetecting unit detecting theillumination intensity, wherein said illumination controlling unit iscontrolled based on a result of detection made by said photodetectingunit so that the brightness of the pattern image of the reference partand the brightness of the pattern image of the part to be inspected,which are obtained by said pattern obtaining unit, match orapproximately match.
 15. The defect inspection apparatus according toclaim 13, further comprising a focusing control parameter setting unitsetting focusing control parameters used for the focusing controlperformed by said focusing controlling unit, wherein: said pattern imageobtaining unit obtains the pattern image of the predetermined part bymaking said observation part changing unit drive the stage or theobjective lens in order to change the observation part of theobservation object to the predetermined part within the observationobject, and by making said focusing controlling unit perform thefocusing control in order to achieve focus on the predetermined partaccording to the focusing control parameters set by said focusingcontrol parameter setting unit; and the focusing control parameters,which are used for the focusing control performed when said patternimage obtaining unit obtains the pattern image of the part to beinspected, are determined based on sample information obtained by thefocusing control performed when said pattern image obtaining unitobtains the pattern image of the reference part.
 16. The defectinspection apparatus according to claim 14, further comprising afocusing control parameter setting unit setting focusing controlparameters used for the focusing control performed by said focusingcontrolling unit, wherein: said pattern image obtaining unit obtains thepattern image of the predetermined part by making said observation partchanging unit drive the stage or the objective lens in order to changethe observation part of the observation object to the predetermined partwithin the observation object, and by making said focusing controllingunit perform the focusing control in order to achieve focus on thepredetermined part according to the focusing control parameters set bysaid focusing control parameter setting unit; and the focusing controlparameters, which are used for the focusing control performed when saidpattern image obtaining unit obtains the pattern image of the part to beinspected, are determined based on sample information obtained by thefocusing control performed when said pattern image obtaining unitobtains the pattern image of the reference part.
 17. A defect inspectionmethod, comprising: driving a stage or an objective lens as opposed toan observation object in order to change an observation part of theobservation object placed on the stage to a reference part determined tobe normal beforehand within the observation object; performing focusingcontrol in order to achieve focus on the reference part; obtaining anintensity of illumination for the observation object; performing imagecapturing, and obtaining a pattern image of the reference part;obtaining exposure and a gain when the image capturing is performed;driving the stage or the objective lens in order to change theobservation part of the observation object to a part to be inspected,which becomes a target of inspecting presence/absence of a defect withinthe observation object; performing focusing control in order to achievefocus on the part to be inspected; illuminating the observation objectwith a same illumination intensity as the obtained illuminationintensity; obtaining a pattern image of the part to be inspected byperforming the image capturing with the same exposure and gain as theobtained exposure and gain; and detecting presence/absence of anabnormal condition of the part to be inspected by making a comparisonbetween the pattern image of the reference part and the pattern image ofthe part to be inspected.